Silver electroplating compositions and methods for electroplating rough matt silver

ABSTRACT

Silver electroplating compositions deposit rough, matt silver having needle-like grain structures. The rough, matt, silver deposits enable good adhesion with dielectric materials, even in environments of high relative humidity.

FIELD OF THE INVENTION

The present invention is directed to silver electroplating compositionsand methods for electroplating rough, matt silver. More specifically,the present invention is directed to silver electroplating compositionsand methods for electroplating rough, matt silver having needle-like orconical-like grain structures to improve adhesion with dielectricmaterials.

BACKGROUND OF THE INVENTION

Lead-frames are used to mount and process semiconductor dice or chips inthe production of semiconductor devices. The Lead-frames electricallyconnect the chip to external devices via leads of the lead-frame. Thereare certain types of the lead-frames in the industry, such as spotsilver/solder-coated lead-frames and palladium pre-plated lead-frames(PPF).

Conventionally, silver plating is applied to the entirety or a part ofthe surface of a lead-frame base. The lead-frame bases are made ofcopper or copper alloy to secure good bonding with metal wires (such asgold wire or copper wire) used at the time of bonding with asemiconductor element. To minimize the undesired diffusion of copper,which resides in the under-lying lead-frame base made of copper orcopper alloy, silver or silver alloy is formed directly on thelead-frame base made of the copper or copper alloy without an undercoatplating layer, such as nickel underlayer. The silver or silver alloylayer can have a thickness of 2 μm or more, typically, of 2.5˜3.0 μm.

After semiconductor chips are mounted onto the lead-frame base, and thebonding wire connections are made between the chips and the lead-framebase, the semiconductor chips are encapsulated with a plastic moldingcompound called epoxy molding compound (EMC) to form a package. For thehigh reliability requirement, a good adhesion between lead-frame baseand the EMC of the package is the key to securing proper functioning ofintegrated circuit (IC) devices. Delamination or cracking of thepackage, and even the so-called “popcorn” effect, results in devicefailure.

During the lifetime of the package, ambient moisture may be absorbed atthe interface between the EMC and the lead-frame base. Moistureabsorption and the retention inside the device results in trapping ofthe moisture which is then vaporized at elevated temperatures. Thevaporizing moisture exerts tremendous internal package stress, which maylead to delamination in the EMC and lead-frame base interface.

To estimate the tendency of a given package to delaminate, Institute forInterconnecting and Packaging Electronic Circuits (IPC) and Solid StateTechnology Association defined a standard classification of moisturesensitivity levels (MSLs) of lead-frame IC devices. According to thisstandard (J-STD-020D), which is a specification in the IPC and SolidState Technology Association, there are 8 levels for expressing themoisture sensitivity of the package. MSL 1 corresponds to packages thatare immune to delamination regardless of the exposure to moisture whileMSL 5 and MSL 6 devices are most prone to moisture induced fracture. Toensure sufficient adhesion under practical conditions, lead-frame ICpackages are tested according to the J-STD-20 MSL standard.

Recent trends toward introducing advanced electronic technologies intoautomobiles has led to a steady increase in the number of automotivesemiconductors. Meanwhile, conventional gold wire is increasingly beingreplaced with lower-cost copper wire to slash semiconductor packagecosts. However, copper wire has a drawback in that it is easily corrodedby an additive containing sulfur atoms that is used for improving theadhesion with the lead-frame. To satisfy strict conditions inreliability tests for automotive conductors specified in the AutomotiveElectronics Council-Q006 (AEC-Q006), it is crucial to prevent thedelamination between EMC and the lead-frame in the reflow process.Furthermore, in other fields such as 5G/Telecom and Storage, there areincreasing requests for MSL-1 compliance (Moisture Sensitivity Level −1,85° C. & 85% relative humidity for 168 hours, J-STD-20). To sum up, theend market demand of IC packages requires a higher reliability and arobust adhesion force between EMC and the lead-frame base.

Typically, the surface of most lead-frame structures consists of twometals, such as copper or a copper alloy from which the lead-frame bodystructure is made, and silver or silver alloy which is present on thesurface of the lead-frame body structure. Silver or an alloy containingsilver often has poor adhesion to EMC. To address adhesion between thelead-frame base and EMC, the industry has mainly focused on the copperor copper alloy surface. This may be achieved by chemical etchingprocesses. For example, chemical etching processes can produce a metaloxide layer on the copper or copper alloy surfaces to improve adhesion,as the metal oxide surfaces generally show better adhesion to EMC thanoxide-free metal surfaces. In addition to chemical etching processes,electrochemical treatments such as by applying an anodic current to thecopper or copper alloy materials can roughen a surface to improveadhesion.

In recent years the industry has focused on reducing the size and costof semiconductor packages. There has been an increasing demand forhigh-density packaging where lighter and smaller parts are required. Thehigh-density packages further compromise adhesion between the copper,copper alloys and silver or silver alloys, specifically within the EMCencapsulation. Accordingly, adhesion between the lead-frame base andEMC, as well as the package reliability, especially with respect tomoisture sensitivity, is substantially compromised.

Therefore, there is a need for a method to improve adhesion betweenlead-frames and EMC in semiconductor packaging.

SUMMARY OF THE INVENTION

The present invention is directed to a silver electroplating compositioncomprising silver ions, a conductivity compound and a compound having aformula:

wherein R₁ is hydrogen or C₁-C₄ alkyl and R₂ is C₁-C₄ alkyl or phenyl.

The present invention is further directed to a method of electroplatingrough, matt silver on a substrate including:

-   -   a) providing the substrate;    -   b) contacting the substrate with a silver electroplating        composition comprising silver ions, a conductivity compound and        a compound having a formula:

wherein R₁ is hydrogen or C₁-C₄ alkyl and R₂ is C₁-C₄ alkyl or phenyl;and

c) applying an electric current to the silver electroplating compositionand the substrate to electroplate a rough matt silver deposit on thesubstrate.

The present invention is further directed to an article comprising arough, matt silver layer adjacent a surface of a substrate, wherein therough, matt silver layer has a Sa of 0.1-0.4 μm and an Sdr of 5-50%.

The silver electroplating composition of the present invention enablesthe electroplating of a rough matt silver deposit on a substrate suchthat the rough matt silver provides good and reliable adhesion withdielectric materials, such as, but not limited to, an epoxy moldingcompound (EMC), even in relatively high moisture environments. The roughmatt silver of the present invention enables secure adhesion withinsemiconductor packaging to inhibit delamination or cracking of thepackage as well as the “popcorn” effect, to prevent IC device failure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a SEM at 5000×taken with a Zeiss microscope of a semi-brightsilver layer electroplated with a conventional silver electroplatingbath.

FIG. 2 is a SEM at 5000×taken with a Zeiss microscope of a matt roughsilver layer electroplated with a silver electroplating bath of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

As used throughout the specification the abbreviations have thefollowing meanings, unless the context clearly indicates otherwise: °C.=degrees Centigrade; g=gram; ppm=parts per million; Kg=kilogram;L=liter; mL=milliliter; mm=millimeters; cm=centimeter; dm=decimeter;μm=microns; nm=nanometers; DI=deionized; A=amperes; ASD=amperes/dm2=plating speed; DC=direct current; N=newtons; mN=milli-newtons;R.O.=reverse osmosis; R.T.=room temperature; v=volts; s=seconds;sec.=seconds; 3D=three dimensional; rpm=revolutions per minute;MSL-1=Moisture Sensitivity Level −1, 85° C. & 85% relative humidity for168 hours; w/o MSL-1=without MSL treatment; w/MSL-1=with MSL treatment;C.D.=current density; Ag=silver; Cu=copper; and S=sulfur.

The term “adjacent” means directly in contact with such that two metallayers have a common interface. The abbreviation “N” means Newtons whichis the SI unit of force and it is equal to the force that would give amass of one kilogram an acceleration of one meter per second per secondand is equivalent to 100,000 dynes. The term “Ra” means arithmetic meandeviation in profile roughness. The term “Sa” means arithmetical meanheight and is substantially equivalent to Ra. The term “Sdr” meansdeveloped interfacial area ratio corresponding to surface ratio with acorrelation of Sdr=(surface ratio −1)×100%. The term “aqueous” meanswater or water-based where organic solvents may be added to helpsolubilize one or more components in a plating composition or platingbath. The terms “composition” and “bath” are used interchangeablythroughout the specification. The terms “deposit” and “layer” are usedinterchangeably throughout the specification. The terms“electroplating”, “plating” and “depositing” are used interchangeablythroughout the specification. The term “matt” means dull or withoutluster but not smokey or foggy in appearance. The term “semi-bright”means that the surface of the article has a haze or slight hazeappearance visually but still reflects light in parallel. The term“bright” means the surface of the article reflects light in parallel andhas a clear appearance visually. The term “morphology” means shape,size, texture or topography of a surface or article. The term“dielectric” means an insulating material of substantially poorelectrical conductivity. The term “haze” means smokey or foggy inappearance. The term “aliquot” means a portion of a larger whole,especially samples taken for chemical analysis or other treatment. The“—” in a chemical structure means an optional covalent chemical bond.The term “thio” means an organic compound which includes —S— or —SH inthe chemical structure. The terms “a” and “an” can refer to both thesingular and the plural throughout the specification. All percent (%)values and ranges indicate weight percent unless otherwise specified.All numerical ranges are inclusive and combinable in any order, exceptwhere it is logical that such numerical ranges are constrained to add upto 100%.

The present invention is directed to silver electroplating compositionscontaining silver ions, a conductivity compound, and a compound having aformula:

wherein R₁ is hydrogen or C₁-C₄ alkyl and R₂ is C₁-C₄ alkyl or phenyl,preferably, R₁ is hydrogen or C₂-C₄ alkyl and R₂ is C₂-C₄ alkyl orphenyl, more preferably, R 1 is hydrogen or C₄ alky and R₂ is C₄ alky orphenyl.

Sources of silver ions can be provided by silver salts such as, but notlimited to, silver halides, such as chloride, bromide and fluoride,silver gluconate, silver citrate, silver lactate, silver nitrate, silversulfates, silver alkane sulfonates, silver alkanol sulfonates, silverpotassium cyanide or mixtures thereof. When a silver halide is used,preferably, the halide is chloride. Preferably, the silver salts aresilver potassium cyanide, silver nitrate, a silver alkane sulfonate, ormixtures thereof, more preferably, the silver salt is silver potassiumcyanide, silver nitrate or mixtures thereof. The silver salts aregenerally commercially available or can be prepared by methods describedin the literature. Preferably, the silver salts are readilywater-soluble. No alloying metals or metals for purposes of brighteningthe silver deposit are included in the silver electroplatingcompositions of the present invention.

Preferably, silver salts are included in the compositions to providesilver ions at concentrations of at least 10 g/L, more preferably,silver salts are included in the compositions in amounts to providesilver ion concentrations in amounts of 10 g/L to 100 g/L, furtherpreferably, silver salts are included in amounts to provide silver ionconcentrations of 20 g/L to 80 g/L, even more preferably, silver saltsare included in amounts to provide silver ions at concentrations of 20g/L to 60 g/L, most preferably, silver salts are included in thecompositions in amounts to provide silver ion concentrations of 30 g/Lto 60 g/L.

Conducting compounds included in the silver electroplating compositionsof the present invention include water-soluble salts to support anelectrical current in the silver electroplating compositions duringelectroplating of silver. Conducting salts include, but are not limitedto, potassium dihydrogen phosphate, sodium dihydrogen phosphate,potassium phosphate, sodium phosphate, ammonium phosphate, sodiumpyrophosphate, potassium pyrophosphate, ammonium pyrophosphate, sodiumnitrate, nitrites, citrates, tartrates, salts of organic acids, salts ofinorganic acids and mixtures of one or more of the foregoing conductivesalts. Preferably, the conducting salts are potassium dihydrogenphosphate, potassium phosphate, sodium phosphate, ammonium phosphate,sodium nitrate or mixtures thereof. More preferably, the conductingsalts are potassium dihydrogen phosphate, sodium nitrate or mixturesthereof. Most preferably, the conducting salt is potassium dihydrogenphosphate.

Organic acids which can be included in the silver electroplatingcompositions of the present invention include, but are not limited to,acetic acid, citric acid, malonic acid, arylsulfonic acids,alkanesulfonic acids, such as methanesulfonic acid, ethanesulfonic acidand propanesulfonic acid, aryl sulfonic acids such as phenylsulfonicacid, tolylsulfonic acid, 5-sulfosalicylic acid. Salts of the foregoingacids also can be included in the silver electroplating compositions ofthe present invention.

Inorganic acids which can be included in the silver electroplatingcompositions of the present invention include, but are not limited to,sulfuric acid, sulfamic acid, hydrochloric acid, phosphoric acid,hydrobromic acid and fluoroboric acid. Water-soluble salts of theforegoing acids also can be included in the silver electroplatingcompositions of the present invention. Mixtures of acids and their saltscan be used. The acids, both organic and inorganic, are generallycommercially available or can be prepared by methods known in theliterature.

Preferably, conducting compounds are included in amounts of at least 50g/L, more preferably, from 50 g/L to 250 g/L, even more preferably, from50 g/L to 150 g/L, most preferably from 80 g/L to 125 g/L.

Compounds having the formula (I) above are included in the silverelectroplating compositions of the present invention as rougheningagents to provide a rough matt silver deposit. Such compounds areincluded in the silver electroplating compositions of the presentinvention, preferably, in amounts of at least 1 ppm, more preferably,from 5-100 ppm, even more preferably, from 5-50 ppm, most preferably,from 5-20 ppm.

The most preferred compounds have the formulae below.

Optionally, one or more buffering agents and pH adjusting agents can beincluded in the silver electroplating compositions to maintain a desiredpH. Buffering agents include, but are not limited to, boric acid, saltsthereof, such as boric acid disodium salt, boric acid potassium salt,boric acid ammonium salt and mixtures thereof, citric acid and salts ofcitric acid, such as potassium, sodium, ammonium salts, or mixturesthereof.

Optional agents for adjusting the pH include, but are not limited to,potassium hydroxide, sodium hydroxide, ammonium hydroxide, citric acid,salts of citric acid, such as potassium citrate, sodium citrate andammonium citrate, phosphates, carbonates, phosphoric acid and mixturesthereof.

Preferably, buffering agents and pH adjusting agents are included in thesilver electroplating compositions in amounts of 10 g/L and greater,more preferably from 15 g/L to 100 g/L, even more preferably, from 15g/L to 70 g/L. Most preferably, boric acid and salts thereof can beincluded in amounts of 15 g/L to 25 g/L. Most preferably, pH adjustingagents can be included in amounts of 30 g/L to 70 g/L.

Preferably, the pH of the silver electroplating compositions of thepresent invention ranges from 6-14, more preferably, from 7-13, evenmore preferably, from 8-12, most preferably, from 8-10.

Optionally, the silver electroplating compositions of the presentinvention include one or more silver complexing agents. Such complexingagents include, but are not limited to, potassium cyanide, hydantoin,hydantoin derivatives, such as 5,5-dimethyl hydantoin, succinimide andderivatives thereof, maleimide and derivatives thereof, and nicotinicacid. A preferred silver complexing agent is potassium cyanide.

Such silver complexing agents are included in conventional amounts whichare well known to those of ordinary skill in the art. Preferably, thesilver complexing agents are included in amounts of at least 5 g/L, morepreferably, 5-100 g/L, even more preferably from 5-50 g/L, mostpreferably, from 5-25 g/L.

Optionally, the silver electroplating compositions of the presentinvention can include one or more conventional grain refiners. Suchgrain refiners can include, but are not limited to, one or more ofthiomalic acid, 2-mercaptosuccinic acid, 3-mercapto-1-propanesulfonicacid, 1-[2-(dimethylamino)ethyl]-1H-tetrazole-5-thiol, and saltsthereof. Preferably, the silver electroplating compositions of thepresent invention exclude such grain refiners.

When the grain refiners are included, they can be included in amounts of5 g/L or greater, more preferably, in amounts of 10 g/L to 100 g/L.

In the silver electroplating compositions of the present invention,water is included as solvent and is, preferably, at least one ofdeionized water and distilled water to limit incidental impurities.

Optionally, the silver electroplating compositions of the presentinvention can include one or more organic solvents to assist insolubilizing composition components in water. Such organic solventsinclude pyridine, pyridine compounds, or mixtures thereof. Preferably,such pyridine compounds consist of 2-pyridinemethanol,3-pyridinemethanol, 2-pyridineethanol, 3-pyridineethanol and mixturesthereof in combination with water. Preferably, when the solvent includesa pyridine compound, the solvent of the silver electroplatingcomposition consists of 3-pyridinemethanol and water. Preferably, suchcompounds are included in the silver electroplating compositions of thepresent invention in amounts of 0.1 g/L to 2 g/L, more preferably, inamounts of 0.2 g/L to 1 g/L, even more preferably, from 0.2 g/L to 0.5g/L.

Optionally, one or more surfactants can be included in the silverelectroplating compositions of the present invention. Such surfactantsinclude, but are not limited to, ionic surfactants such as cationic andanionic surfactants, non-ionic surfactants, and amphoteric surfactants.Surfactants can be included in conventional amounts such as 0.05 g/L to30 g/L.

Examples of anionic surfactants are sodium di(1,3-dimethylbutyl)sulfosuccinate, sodium-2-ethylhexylsulfate, sodium diamylsulfosuccinate, sodium lauryl sulfate, sodium lauryl ether-sulfate,sodium di-alkylsulfosuccinates and sodium dodecylbenzene sulfonate.Examples of cationic surfactants are quaternary ammonium salts such asperfluorinated quaternary amines.

Other optional additives can include, but are not limited to, levelersand biocides. Such optional additives can be included in conventionalamounts.

Preferably, the silver electroplating compositions consist of water,optionally pyridine, 2-pyridinemethanol, 3-pyridinemethanol,2-pyridineethanol, 3-pyridineethanol, or mixtures thereof, silver ions,counter anions, a conducting compound, a compound of formula (I),optionally a buffering agent, optionally a pH adjusting agent,optionally an acid, optionally a grain refiner, optionally a surfactant,optionally a leveler, optionally a biocide and a pH of 6-14.

More preferably, the silver electroplating compositions consist ofwater, optionally 2-pyridinemethanol, 3-pyridinemethanol,2-pyridineethanol, 3-pyridineethanol, or mixtures thereof, silver ions,counter anions, a conducting compound, a compound selected from thegroup consisting of 6-(dibutylamino)-1,3,5-triazine-2,4-dithiol,6-amino-1,3,5-triazine-2,4-dithiol and mixtures thereof, optionallyboric acid or salt thereof, optionally potassium hydroxide, sodiumhydroxide, ammonium hydroxide or mixtures thereof, optionally an acid,optionally a surfactant, optionally a leveler, optionally a biocide anda pH of 7-13.

Even more preferably, the silver electroplating compositions consist ofwater, optionally 3-pyridinemethanol, silver ions, counter anions, aconducting compound, a compound selected from the group consisting of6-(dibutylamino)-1,3,5-triazine-2,4-dithiol,6-amino-1,3,5-triazine-2,4-dithiol and mixtures thereof, optionallyboric acid or salt thereof, optionally potassium hydroxide, sodiumhydroxide, ammonium hydroxide or mixtures thereof, optionally asurfactant, optionally a leveler, optionally a biocide and a pH of 8-12.

Most preferably, the silver electroplating compositions consist ofwater, optionally 3-pyridinemethanol, silver ions, counter anions, aconducting compound, a compound selected from the group consisting of6-(dibutylamino)-1,3,5-triazine-2,4-dithiol,6-amino-1,3,5-triazine-2,4-dithiol and mixtures thereof, optionallyboric acid or salt thereof, optionally potassium hydroxide, sodiumhydroxide, ammonium hydroxide or mixtures thereof, optionally asurfactant, optionally a leveler, optionally a biocide and a pH of 8-10.

The silver electroplating compositions of the present invention can beused to deposit rough, matt silver layers on various substrates.Preferably, the substrates on which rough, matt silver layers aredeposited include copper and copper alloy layers. Such copper alloylayers include, but are not limited to, brass and bronze. Preferably,the silver electroplating compositions of the present invention are usedto plate rough, matt silver layers adjacent copper and copper alloylayers. Preferably, such copper and copper alloy layers are included inlead-frame fabrication and IC semiconductor packaging. Preferably, therough, matt silver layer is electroplated adjacent a silver strike layerwhich is adjacent to the copper or copper alloy of the lead frame baseor substrate. Such silver strike layers, preferably, range from 10-20nm. Silver strike layers are deposited adjacent the copper or copperalloy by using conventional silver electroplating baths or byelectroless silver metal plating baths. A dielectric material called anepoxy molding compound is used to encase the lead-frame with the silverlayers and copper or copper alloy to complete the lead-frame and ICsemiconductor package. The IC packages which include the rough, mattsilver layers of the present invention enable good adhesion with epoxymolding compounds to prevent delamination of molding compounds and canbe expected to have MSL-1 compliance (Moisture Sensitivity Level −1, 85°C. & 85% relative humidity for 168 hours, J-STD-20).

The silver electroplating compositions of the present invention can beelectroplated at temperatures from room temperature to 70° C.,preferably, from 30° C. to 60° C., more preferably, from 40° C. to 60°C. The silver electroplating compositions are preferably undercontinuous agitation during electroplating.

The silver electroplating method of the present invention includesproviding a substrate, providing the silver electroplating compositionand contacting the substrate with the silver electroplating compositionsuch as by immersing the substrate in the composition or spraying thesubstrate with the composition. Applying a current with a conventionalrectifier where the substrate functions as a cathode and there ispresent a counter electrode or anode. The anode can be any conventionalsoluble or insoluble anode used for electroplating silver to depositadjacent a surface of a substrate.

Current densities for electroplating the rough, matt silver can rangefrom 5 ASD or higher. Preferably, the current densities range from 10ASD to 180 ASD, further preferably, from 20 ASD to 150 ASD, even morepreferably, from 100 ASD to 150 ASD. Preferably, high current densitiesare used to plate silver to achieve the desired rough, matt silverdeposit.

The silver electroplating compositions of the present invention enabledeposition of rough matt and uniform silver layers. The silver contentof the deposits is greater than or equal to 99% silver by metals basis.

The rough, matt silver layers have a Sa of, preferably, 0.1-0.4 μm, morepreferably, 0.2-0.3 μm and an Sdr of, preferably, 5-50%, morepreferably, 25-30%. The Sa and Sdr can be measured for silver layersusing conventional methods and apparatus used to measure surfaceroughness known to those of ordinary skill in the art. One method is touse an Olympus 3D Laser Microscope-LEXT OLS5000-LAF (available fromOlympus Scientific Solutions Americas). The surface roughness can bescanned on a surface area of, for example, 2561 m×2561 m with50×objective magnification.

The rough, matt silver deposits have needle-like or acicular-likestructures with peak heights ranging from 1-41 m and diameters at peakbase of 0.2-0.41 m. Such parameters can be measured using an Olympus 3DLaser Microscope-LEXT OLS5000-LAF. Other methods and apparatus can beused as are well known to those of ordinary skill in the art.

Preferably, the thickness of the rough, matt silver layer ranges from0.1 μm or greater. Further preferably, the rough matt silver layer has athickness range of 0.1 μm to 10 μm, more preferably, from 0.5 μm to 5μm, even more preferably, from 2 μm to 4 μm, most preferably, from 2 μmto 3 μm. Thickness can be measured by conventional methods known tothose of ordinary skill in the art. For example, thickness of the silverlayers can be measured using a Bowman Series P X-Ray Fluorimeter (XRF)available from Bowman, Schaumburg, IL. The XRF can be calibrated usingpure silver thickness standards from Bowman.

The following examples are included to further illustrate the inventionbut are not intended to limit its scope.

Example 1 Button Shear Test

A plurality of copper coupons was provided having dimensions of 0.27dm×0.06 dm×2 sides to provide an area of each coupon of 0.032 dm 2. TheSa and Sdr of the copper coupons were determined using an Olympus 3DLaser Microscope-LEXT OLS5000-LAF. The Sa ranged from 0.076-0.085 μm.The average was 0.08 μm. The Sdr ranged from 1.26-1.49%. The average was1.40%.

An aliquot of the copper coupons was roughened according to theprocedure described in Tables 1 and 2.

TABLE 1 Component Amount CIRCUBOND ™ Treatment 180C¹  140 mL/LCIRCUBOND ™ Treatment 180B¹  1.6 mL/L 35% Hydrogen Peroxide   25 mL/L DIWater To one Liter ¹CIRCUBOND ™ products are available from Rohm andHaas Electronic Materials LLC.

TABLE 2 Operating Parameter Condition Temperature 35-39° C. Immersiontime 1 minute Agitation Stirring Post Treatment DI Water Rinsing

Sa and Sdr of the roughened copper coupons were measured with an Olympus3D Laser Microscope-LEXT OLS5000-LAF. The Sa values ranged from0.199-0.242 μm with a mean value of 0.218 μm. The Sdr values ranged from18.5-23.9% with a mean value of 20.7%.

A second and third aliquot were electroplated with a silver layer from aconventional silver plating bath or a matt rough silver layer with asilver electroplating bath of the invention described below. A fourthaliquot of copper coupons was not roughened nor silver electroplated.

TABLE 3 Process Metallization on Copper Coupons Current Chemical(current Step # Process Bath Concentrations density) Temperature Time 1Electro- Ronaclean ™  60 g/L 4~6 v 60° C. 30 sec. cleaning¹ GP-300 2Rinsing R.O. Water — — R.T.  5 sec. 3 Activation² Actronal ™ 100 g/L —R.T.  5 sec. 988 solution 4 Rinsing R.O. Water — — R.T.  5 sec. 5 SilverPotassium 2.4 g/L and 100  0.2 A R.T. 20 sec. Strike silver g/L,  (1.5ASD) cyanide and respectively Potassium cyanide in water 6 Rinsing R.O.Water — — R.T.  5 sec. 7 Silver Silverjet³ See Tables 4-5 2.56 A 60° C.3.0 sec.  Plating by 220 SE  (100 ASD) Jet plater and Rough Matt Silver8 Rinsing R.O. Water — — R.T.  5 sec. 9 Drying By hot gun — — — —¹Ronaclean ™ GP-300 Solution is available from Rohm and Haas ElectronicMaterials LLC. ²Actronal ™ 988 Solution is available from Rohm and HaasElectronic Materials LLC. ³Silverjet ™ 220 SE Silver Electroplating Bathand products are available from Rohm and Haas Electronic Materials LLC.

Silver strike was electroplated on the copper coupons to a thickness of0.1-0.2 μm. The thickness of the silver strike layer was measured with aBowman Series P X-Ray Fluorimeter (XRF). Silver plating was done in a 1L plastic container using an insoluble stainless steel anode.

TABLE 4 (Invention) Rough Matt Silver Bath Components Amount Potassiumsilver cyanide (silver ions) 74 g/L (40 g/L) Boric acid  25 g/LPotassium hydroxide  54 g/L Potassium dihydrogen phosphate 100 g/L6-Anilino-1,3,5-triazine-dithiol 10 ppm Water To 1 Liter

Silver electroplating was done at a pH of 9-9.5. A jet plater for highspeed silver plating was used (1010 Spot Plating Machine by Kam TsuenMechanical & Electrical Ltd.). The silver layer had a thickness of 2.5-3μm as measured using a Bowman Series P X-Ray Fluorimeter (XRF) availablefrom Bowman, Schaumburg, IL. The XRF was calibrated using pure silverthickness standards from Bowman.

TABLE 5 (conventional bath) Semi-Bright Silver Bath (Silverjet ™ 220SE⁴) Components Amount Potassium silver cyanide (silver ions) 74 g/L (40g/L) Silverjet ™ Make-Up Solution (conductivity 500 mL/L salt + buffer)Silverjet ™ Conditioner (surfactant)  0.5 mL/L  Silverjet ™ 220Brightener (grain refiner)  5 mL/L Silverjet ™ Special Additive(anti-immersion  5 mL/L agent) Water To 1 Liter ⁴Silverjet ™ 220 SESemi-Bright Silver Bath and products are available from Rohm and HaasElectronic Materials LLC. The formulation is free of the compounds6-anilino1,3,5-triazine-2,4-dithiol and6-(dibutylamino)-1,3,5-triazine-2,4-dithiol.

Silver electroplating was done at a pH of 9-9.5. The silver layer had athickness of 2.5-3 μm as measured by the Bowman Series P X-RayFluorimeter (XRF). The XRF was calibrated using pure silver thicknessstandards from Bowman.

The Sa and Sdr were measured for the silver layers from each of the twotypes of silver electroplating baths. The surface roughness was analyzedusing an Olympus 3D Laser Microscope-LEXT OLS5000-LAF (available fromOlympus Scientific Solutions Americas). The surface roughness wasscanned on a surface area of 256 μm×256 μm with 50× objectivemagnification.

The semi-bright silver layers plated from the Silverjet™ 220 SE SilverElectroplating Bath had Sa values ranging from 0.09-0.12 μm and Sdrvalues ranging from 0.5-1.7%. FIG. 1 is a SEM at 5000× of a surface of asilver layer from one of the silver plated coupons taken with a Zeissmicroscope.

In contrast, the Sa values of the silver surface plated on the coppercoupons from the silver electroplating bath of the invention ranged from0.15-0.3 μm and had an Sdr ranging from 12-30%. FIG. 2 is a SEM at 5000×of a surface of a silver layer from one of the silver plated couponstaken with a Zeiss microscope. The silver surface of FIG. 2 has a roughand acicular morphology in contrast to that of FIG. 1 . The silverelectroplating bath of the invention had a substantially rougher silverdeposits than the silver layers plated from the conventional silverplating bath.

All the coupons were then coated with molding compound EME-, a mixtureof epoxy resin (5-10%), phenol resin (1-5%), amorphous silica A(70-80%), amorphous silica B (5-10%) and carbon black (0.1-1%). Themolding compound was molded into a button shape and cured at 175° C. ina conventional oven for 120 sec. The coupons with the button shapedmolding compound were then post-mold cured at 175° C. for 4 hours. Thecoupons were cooled to room temperature. Half of the coupons with thebutton shaped molding underwent exposure to Moisture Sensitivity Level−1, 85° C. & 85% relative humidity for 168 hours using EXPEC bench-toptype Temperature & Humidity Chamber, model SH-221. The coupons wereplaced in a stainless steel basket in the chamber and set at 85° C. atrelative humidity of 85% for the 168 hours (7 days). The coupons werethen removed from the chamber and dried in the ambient environment.

The button shear test was then done on all the coupons. The button sheartest conditions are below:

-   -   a) Shear equipment: 4000 Multipurpose Bondtester available from        Nordson    -   b) Cartridge: DAGE-4000-DG100KG    -   c) Button height: 3 mm    -   d) Button diameter: 3 mm    -   e) Shear height: 20% of button=600 μm    -   f) Shear speed: 85 μm/s    -   g) Temperature: Room temperature

The results of the button shear test for the silver plated coppercoupons, the roughened copper and the un-roughened copper are in Table 6below.

TABLE 6 Rough Conventional Matt Ag Ag Shear Rough Cu Untreated CuTreatment Shear Force Force Shear Force Shear Force w/o MSL-1 31.3 Kg19.6 Kg 25.5 Kg   26 Kg w/MSL-1   27 Kg 16.5 Kg 23.1 Kg 20.4 Kg Diff. %of −13.7% −15.8% −9.4% −21.5% Shear Force

For the treatment w/o MSL-1, the shear force for the rough matt silverwas 31.3 Kg while the shear force for the conventional silver was 19.6kg. The increment was (31.3 Kg-19.6 Kg)/19.6 Kg×100=59.7%. For thetreatment w/MSL-1, the shear force for the matt rough silver was 27 Kgand the conventional silver was 16.5 Kg. The increment was (27 Kg-16.5Kg)/16.5 Kg×100=63.6%. The results showed that the rough matt silverplated from the rough matt silver bath had a high and improved moldingshear force over the silver plated from the conventional silver bath.For the w/o MSL-1, the shear force of the rough matt silver had animproved molding shear force of almost 60%. For the w/MSL-1, the shearforce of the rough matt silver of the invention had an improved moldingshear force of 63.6%. The shear force of the rough matt silver was alsohigher than that of the rough copper surface and the untreated coppersurface.

Although there was adhesion force reduction after MSL-1 treatment of therough matt silver, it was still higher than the conventional silverdeposit, the roughened copper surfaces and the untreated coppersurfaces. The rough matt silver enhanced adhesion between moldingmaterial and silver surface coatings, even under high moistureenvironments.

Example 2 Roughness Analysis of Silver Layers at High ElectroplatingSpeeds

A plurality of C194 copper coupons with dimensions of 0.27 dm×0.25 dmwere provided. The C194 coupons are a type of semiconductor materialused to form lead-frames. The C194 coupons were composed of copper(>97%), iron (2.1-2.6%), phosphorous (0.015-0.15%) and zinc (0.05-0.2%).Silver plating area on the coupons was 0.0256 dm 2 (0.16 dm×0.16 dm).

TABLE 7 Process Metallization on Copper Coupons Current Chemical(Current Step# Process Bath Concentration Density) Temperature Time 1Electro- Ronaclean ™  60 g/L 4~6 v 60° C. 30 sec. cleaning GP-300 2Rinsing R.O. Water — — R.T.  5 sec. 3 Activation Actronal ™ 100 g/L —R.T.  5 sec. 988 solution 4 Rinsing R.O. Water — — R.T.  5 sec. 5 SilverPotassium 2.4 g/L and  0.2 A R.T. 20 sec. Strike silver 100 g/L,  (1.5ASD) (0.2-0.3 cyanide, and respectively μm) potassium cyanide in water 6Rinsing R.O. Water — — R.T.  5 sec. 7 Aqueous See Table 8 See Table 83.84 A 60° C. 2.0 sec.  Silver  (150 ASD) 1.8 sec.  Plating by 4.61 AJet plater  (180 ASD) 8 Rinsing R.O. Water — — R.T.  5 sec. 9 Drying (Byhot gun) — — — —

TABLE 8 Aqueous Silver Electroplating Baths In- In- In- In- ControlControl vention vention vention vention Component Bath 1 Bath 2 Bath 1Bath 2 Bath 3 Bath 4 Potassium 74 g/L 74 g/L 74 g/L 74 g/L 74 g/L 74 g/Lsilver cyanide (40 g/L) (40 g/L) (40 g/L) (40 g/L) (40 g/L) (40 g/L)(Ag+) Boric acid 50 g/L 50 g/L 50 g/L 50 g/L 50 g/L 50 g/L Potassium 22g/L 31 g/L 22 g/L 22 g/L 31 g/L 31 g/L hydroxide Potassium — — 80 g/L 80g/L — — nitrate Potassium — — — — 50 g/L 50 g/L dihydrogen phosphate6-anilino- — — 10 ppm — 10 ppm — 1,3,5-triazine- 2,4-thiol 6- — — — 10ppm — 10 ppm (dibutylamino)- 1,3,5-triazine- 2,4-dithiol Water To 1 L To1 L To 1 L To 1 L To 1 L To 1 L

The pH of the baths was 9-9.5. Electroplating was done with a jet plateras in Example 1 above. Control bath 1 and invention baths 1-2 wereplated at 150 ASD and control bath 2 and invention baths 3-4 were platedat 180 ASD. A semi-bright silver deposit was plated on copper couponsplated with control baths 1 and 2. A rough matt silver deposit wasplated on copper coupons plated with invention baths 1-4. The thicknessof the silver deposits was 2.5-3 μm.

The surface roughness was measured using an Olympus 3D LaserMicroscope-LEXT OLS5000-LAF as described in Example 1 above. The Sa andSdr values for the plated coupons are in the table below.

TABLE 9 Roughness Analysis Current Density Bath (ASD) Sa Sdr Control 1150 0.168 15.8% Control 1 180 0.294   30% Control 2 150 0.157 14.7%Control 2 180 0.290 29.4% Invention 1 150 0.225 21.5% Invention 1 1800.37   38% Invention 2 150 0.21 19.6% Invention 2 180 0.418 39.6%Invention 3 150 0.233   24% Invention 3 180 0.36 39.6% Invention 4 1500.277 31.8% Invention 4 180 0.415 43.4%

The results of the roughness analysis showed that the silver depositsplated from the baths of the present invention had substantially roughersurfaces than the silver deposits plated from the control orconventional silver baths when plated at current densities of 150 ASDand 180 ASD.

Example 3 Hull Cell Test for Silver Electroplating Baths Containing ThioOrganic Compounds as Roughening Agents

A plurality of brass panels having dimensions 10 cm×7.5 cm with aplating area of 10 cm×5 cm was provided for silver electroplating inHull cells with a current density range of 20-50 ASD. The brass panelswere treated for plating and silver electroplated according to theprocess described in Table 10 below.

TABLE 10 Current Chemical Concen- (Current Temper- Step# Process Bathtration Density) ature Time 1 Electro- Ronaclean ™  60 g/L 4 v 60° C. 30sec. cleaning GP-300 2 Rinsing R.O. Water — — R.T.  5 sec. 3 ActivationSulfuric acid 10% — R.T. 10 sec. solution 4 Rinsing R.O. Water — — R.T. 5 sec. 5 Silver Potassium 2.4 g/L or  2 A R.T. 20 sec. Strike silver100 g/L (1.3 (0.2- cyanide or ASD) 0.3 μm) potassium cyanide 6 RinsingR.O. Water — — R.T.  5 sec. 7 Aqueous See Table See 10 A 60° C. 15 sec.Silver 11 Table 11 Plating by Jet plater 8 Rinsing R.O. Water — — R.T. 5 sec. 9 Drying (By hot gun) — — — —

TABLE 11 Aqueous Silver Electroplating Baths Component ConcentrationPotassium silver cyanide [Ag+] 111 g/L [60 g/L] Potassium nitrate 80 g/LBoric acid 50 g/L Potassium hydroxide 22 g/L Thio compound (rougheningagent) 5 ppm or 10 ppm Water To 1 L

TABLE 12 Hull Cell Silver Electroplating Parameters Parameter AmountHull cell current density 20-50 ASD Current 10 A Plating time 15 sec.Plating temperature 60° C. Agitation 520 rpm by propeller stirringPlating bath pH 9~9.5 Silver layer thickness 2.5-3 μm

After the panels were plated with silver and dried, they were inspectedwith the naked eye for appearance. Silver layers which appearedsemi-bright to bright and hazy indicated a substantially smooth surface.Silver layers which appeared matt or dull indicated a substantiallyrough surface. The plating results are disclosed in Table 13.

TABLE 13 Silver Appearance Silver Appearance at 5 ppm of Thio at 10 ppmof Thio BATH # Thio Compound Compound Compound 0 None (control)Semi-bright (no Semi-bright (no compound) compound)  1 (invention)6-Anilino-1,3,5-triazine- Matt Matt 2,4-dithiol  2 (invention)6-(Dibutylamino)-1,3,5- Matt Matt triazine-2,4-dithiol  3 (comparative)4(5)-Imidazole Bright Bright dithiocarboxylic acid  4 (comparative)Bis(carboxymethyl) Semi-bright to Semi-bright to trithiocarbonate brightbright  5 (comparative) 2-Mercaptobenzothiazole Haze to semi-bright Hazeto semi-bright  6 (comparative) 5-Amino-1,3,4- Semi-bright Semi-brightthiadiazole-2-thiol  7 (comparative) 2,5-Dimercapto-1,3,4- Semi-brightSemi-bright thiadiazole  8 (comparative) N,N- Semi-bright Not Availabledimethyldithiocarbamic acid-Na-Salt  9 (comparative) 2-Thiouracil BrightBright 10 (comparative) 1-Allyl-2-thiourea Bright band Bright band 11(comparative) 1-phenyl-2-thiourea Bright band Bright band 12(comparative) Diphenylthiocarbazone Haze to semi-bright Haze tosemi-bright 13 (comparative) 2- Semi-bright Semi-brightMercaptobenzimidazole 14 (comparative) 2-Mercapto-1-methyl- Semi-brightSemi-bright imidazole 15 (comparative) 4,5-Diamino-6-hydroxy-Semi-bright Semi-bright 2-mercaptopyrimidine 16 (comparative)2-Thiobarbituric acid Semi-bright Semi-bright 17 (comparative)1H-1,2,4-Triazole-3-thiol Semi-bright Semi-bright 18 (comparative)3-Amino-1,2,4-triazole-5- Semi-bright Semi-bright thiol 19 (comparative)5-Mercapto-1H-tetrazole- Semi-bright Semi-bright 1-methanesulfonic acid,disodium salt 20 (comparative) 5-Mercapto-(1H)- Semi-bright Semi-brighttetrazolylacetic acid Sodium salt 21 (comparative) 5-Merpcato-1-Semi-bright Semi-bright methyltetrazole (5-Merpcato-1-methyl-1H-tetrazole) 22 (comparative) 1-(4-Hydroxyphenyl)- Semi-brightSemi-bright 1H-tetrazole-5-thiol 23 (comparative)5-(3-Pyridyl)-4H-1,2,4,- Semi-bright Semi-bright triazole-3-thiol 24(comparative) 2-Mercapto-5- Semi-bright Semi-brightbenzimidazolesulfonic acid sodium salt dihydrate 25 (comparative)2-Aminothiazole Semi-bright Semi-bright

Only the silver electroplating baths which included6-anilino-1,3,5-triazine-2,4-dithiol and6-(dibutylamino)-1,3,5-triazine-2,4-dithiol provided a substantiallyrough matt silver deposit.

1.-15. (canceled)
 16. An article comprising a rough, matt silver layeradjacent a surface of a substrate, wherein the rough, matt silver layerhas a Sa of 0.1-0.4 μm and an Sdr of 5-50%.
 17. The article of claim 16,wherein the surface of the substrate is copper or copper alloy.